I have not seen any rumors that Skylake-H (the specific Skylake parts suitable for a 15" MacBook Pro) will be released during 2015. I have no reason to believe that a Skylake MBP will be released before early-2016.
Absolutely not. That would have created confusion about which is the high-end machine: the 15" rMBP and the 17" cMBP as well as confusion about why there was no 17" rMBP. From a marketing perspective, that would have been disastrous. The recently introduced (or re-introduced) Retina MacBook is a perfect example.
That's not clear. It seems that 17" MBP sales were satisfactory at the time of discontinuation. The reason for the discontinuation is that in 2012 the cost of Retina 17" displays was unaffordable due to low yields. Now 17" Retina displays are affordable making a 17" rMBP a realistic possibility.
The version of Skylake suitable for the 15" MBP is Skylake-H. I haven't seen any rumors that suggest Skylake-H might ship before 2016, so any 15" MBP introduced at WWDC is virtually certain to have a Broadwell CPU. I will probably buy one. I presently have no intention of waiting for Skylake, which is only a Tock. The idea that Skylake could 60% more energy efficient that Broadwell, both of which are built on the same 14nm process (the main determinant of energy...
Apple have enough market power to get the chips they want from Intel, whether or not they have been released to the market. Apple have shipped unreleased (to the public) chips before. Yes, it means that we will not see Skylake MBPs until early-2016.